For thousands of years, sand and
gravel have been used in the construction of roads and buildings.
Today, demand for sand and gravel continues to increase.
Mining operators, in conjunction with cognizant resource agencies, must work to ensure that sand mining is conducted in a responsible manner.
Excessive instream sand-and-gravel mining causes the degradation of rivers.
Instream mining lowers the stream bottom, which may lead to bank erosion.
Depletion of sand in the streambed and along coastal areas causes the deepening
of rivers and estuaries, and the enlargement of river mouths and coastal inlets.
It may also lead to saline-water intrusion from the nearby sea.
The effect of mining is compounded by the effect of sea level rise.
Any volume of sand exported from streambeds and coastal areas is a loss to the system.
Excessive instream sand mining is a threat to bridges, river banks and nearby structures. Sand mining also affects
the adjoining groundwater system and the uses that local people make of the river.
Instream sand mining results in the destruction of aquatic and riparian habitat through large changes in the channel morphology.
Impacts include bed degradation, bed coarsening, lowered water tables near the streambed, and channel instability.
These physical impacts cause degradation of riparian and aquatic biota and may lead to the undermining of bridges and other structures.
Continued extraction may also cause the entire streambed to degrade to the depth of excavation.
Sand mining generates extra vehicle traffic, which negatively impairs the environment.
Where access roads cross riparian areas, the local environment may be impacted.
1.1 Sand Budget
Determining the sand budget for a particular stream reach requires site-specific topographic, hydrologic, and hydraulic information.
This information is used to determine the amount of sand that can be removed from the area without causing
undue erosion or degradation, either at the site or at a nearby location, upstream or downstream.
In-channel or near-channel sand-and-gravel mining changes the sediment budget, and may result
in subtantial changes in the channel hydraulics.
These interventions can have variable effects on aquatic habitat, depending on the magnitude and
frequency of the disturbance, mining methods, particle-size characteristics of the sediment,
the characteristics of riparian vegetation,
and the magnitude and frequency of hydrologic events following the disturbance.
Temporal and spatial responses of alluvial river systems are a function of geomorphic thresholds,
feedbacks, lags, upstream or downstream transmission of disturbances, and geologic/physiographic controls.
Minimization of the negative effects of sand-and-gravel mining requires a detailed
understanding of the response of the channel to mining disturbances.
Decisions on where to mine, how much and how often require the definition of a reference state,
i.e., a minimally acceptable or agreed-upon physical and biological condition of the channel.
Present understanding of alluvial systems is generally not sufficient
to enable the prediction of channel responses quantitatively and with confidence; therefore, reference states
are difficult to determine.
Still, a general knowledge of fluvial processes can provide guidelines to minimize the detrimental effects of mining.
Well-documented cases and related field data are required
to properly assess physical, biological, and economic tradeoffs.
1.2 Riparian Habitat, Flora and Fauna
Instream mining can have other costly effects beyond the immediate mine sites. Many hectares of fertile
streamside land are lost annually, as well as
valuable timber resources and wildlife habitats in the riparian areas. Degraded stream habitats result in lost of fisheries productivity,
biodiversity, and recreational potential. Severely degraded channels may lower land and aesthetic values.
All species require specific habitat conditions to ensure long-term survival. Native species in streams are uniquely adapted to
the habitat conditions that existed before humans began large-scale alterations.
These have caused major habitat disruptions that favored some species over others and caused overall declines in biological
diversity and productivity. In most streams and rivers, habitat quality is strongly linked to the stability of channel
bed and banks. Unstable stream channels are inhospitable to most aquatic species.
Factors that increase or decrease sediment supply
often destabilize bed and banks and result in dramatic channel readjustments. For example, human activities that accelerate stream
bank erosion, such as riparian forest clearing or instream mining, cause stream banks to become net sources of
sediment that often
have severe consequences for aquatic species. Anthropogenic activities that artificially lower stream bed elevation cause bed instabilities that
result in a net release of sediment in the local vicinity. Unstable sediments simplify and, therefore, degrade stream habitats for many
aquatic species. Few species benefit from these effects.
The most important effects of instream sand mining on aquatic habitats are bed degradation and sedimentation, which can
have substantial negative effects on aquatic life. The stability of sand-bed and gravel-bed streams depends on a delicate
balance between streamflow, sediment supplied from the watershed, and channel form. Mining-induced changes in sediment supply
and channel form disrupt channel and habitat development processes. Furthermore, movement of unstable substrates results in downstream
sedimentation of habitats. The affected distance depends on the intensity of mining,
particles sizes, stream flows, and channel morphology.
The complete removal of vegetation and destruction of the soil profile destroys habitat both above and below the ground as well
as within the aquatic ecosystem, resulting in the reduction in faunal populations.
Channel widening causes shallowing of the streambed,
producing braided flow or subsurface intergravel flow in riffle areas, hindering movement of fishes between pools. Channel reaches
become more uniformly shallow as deep pools fill with gravel and other sediments, reducing habitat complexity, riffle-pool structure,
and numbers of large predatory fishes.
1.3 Stability of Structures
Sand-and-gravel mining in stream channels can damage public and private property. Channel incision caused by gravel mining can undermine bridge piers
and expose buried pipelines and other infrastructure.
Several studies have documented the bed degradation caused by the two general forms of instream mining: (1) pit excavation and (2) bar skimming.
Bed degradation, also known as channel incision, occurs through two primary processes: (1) headcutting, and (2)"hungry" water. In headcutting,
excavation of a mining pit in the active channel lowers the stream bed, creating a nick point that locally steepens channel
slope and increases flow energy. During high flows, a nick point becomes a location of bed erosion that gradually moves upstream (Fig. 1).